The present invention relates to roofing membranes exhibiting high strength and performance through the incorporation of novel composite reinforcements. Particular applications are found in association with bituminous roofing membranes including these reinforcements.
Bituminous roofing membranes are conventionally built upon a substrate to provide strength to the bituminous materials. Prior art substrates with a composite nature have included multiple layers of pre-manufactured reinforcements such as woven scrims, non-woven scrims, mats, and veils. A preferred material in many of these reinforcements is fiberglass yarn. The composite nature of these prior art reinforcing substrates has been achieved by joining layers thereof with adhesives, sewing the layers together or knitting the layers together. The composite reinforcement substrate is then saturated and coated with the bituminous material so that a substantially continuous matrix of the bitumen surrounds and encloses the substrate.
Some examples of prior art teachings of the use of adhesives to combine multiple layers of reinforcement materials, followed by conversion into roofing products are provided by these United States patents: U.S. Pat. No. 4,491,617; U.S. Pat. No. 4,539,254; U.S. Pat. No. 4,762,744; U.S. Pat. No. 4,780,350; and U.S. Pat. No. 5,108,831. Similarly, the concept of sewing or knitting the reinforcement materials, followed by conversion into roofing products are provided by U.S. Pat. Nos. 5,474,838 and 5,569,430.
Fiberglass yarns, especially high performance fiberglass yarns, have been the material of choice for forming reinforcement materials for this application. For example, a non-woven fiberglass yarn scrim is described in U.S. Pat. No. 3,728,195. Other teachings use fiberglass yarn in woven scrims, which consist of the yarn in a typical leno weave construction. A leno weave differs from a plain weave (in which the warp and filling yarns cross alternately) in that it is a locking-type weave in which two or more warp yarns cross over each other and interlace with one or more filling yarns. The leno weave primarily prevents the shifting of the yarns in an open fabric. While structurally effective, the cost of a high strength high performance fiberglass yarn for forming a composite reinforcement can be prohibitively high. Fiberglass yarns, as the name indicates, are not monofilamentous strands of fiberglass. Instead, a single fiberglass yarn comprises multiple individual strands or filaments of fiberglass, which have been processed into the yarn configuration by steps such as twisting, chemical finishing, etc. While not a staple material, the processing steps involved in creating the yarn create a material with different properties than those exhibited by a monofilamentous product. When sold commercially, fiberglass yarns are typically graded in terms of xe2x80x9cyieldxe2x80x9d, which is a unit of measure indicating the number of lineal yards of the fiber provided by a pound of glass. In this manner, xe2x80x9cyieldxe2x80x9d is effectively inversely proportional to the term xe2x80x9cdenierxe2x80x9d as used in association with fibers such as NYLON, since denier indicates the weight of the material required to provide a given lineal length (9000 m) of the fiber. Roofing scrims have conventionally been provided using fiberglass yarns of 1800, 3700 and 7500 yields, the higher yield number defining a lighter yarn.
It is, therefore, an advantage of the present invention to provide a composite reinforcement having strength and performance comparable to fiberglass yarn, but which has a much lower cost.
This and other advantages of the present invention are provided by a composite reinforcement substrate for a bituminous roofing material, comprising a carrier web and first and second sets of rovings bundles. The carrier web has a pair of opposed planar surfaces and it defines both a machine direction and a cross machine direction for the substrate to be created. The first set of rovings bundles comprises individual rovings with longitudinal axes positioned in spaced apart parallel relationship atop one of the planar surfaces of the carrier web and the second set of rovings bundles comprising individual rovings with longitudinal axes positioned in spaced apart parallel relationship to each other, but in an angular non-parallel relationship to the longitudinal axes of the first set of rovings bundles. The second set of rovings bundles will either rest directly on one of the planar surfaces of the carrier web or on the first set of rovings bundles. The first and second sets of rovings bundles and the carrier web are secured together in a fashion which maintains each set of bundles in the spaced apart parallel relationships and maintains the two sets in the angular non-parallel relationship.
The sets of rovings bundles may be secured to the carrier web and to each other with a conventional adhesive, with a stitch bonded yarn, or by other conventional means. If stitch bonding is used, the preferred yarn would be polyester yarn.
In one embodiment, the first set of rovings bundles is positioned parallel to the cross machine direction of the carrier web and the second set of rovings bundles is positioned parallel to the machine direction of the carrier web.
In one embodiment, the carrier web is formed from a polyester and has a weight in the range from about 0.5 to about 2.0 ounces per square yard.
In one embodiment, the first and second set of rovings bundles will comprise individual fiberglass rovings of 1800 yield or heavier, and even more preferably, of 600 yield or heavier.